1. Field of the Invention
The present invention relates to an image signal data generator for generating and outputting image signal data having synchronizing signal patterns corresponding to prescribed image signal formats.
2. Description of the Prior Art
In an image signal data generator which outputs image signal data processed digitally, a process of superposing synchronizing signal data such as horizontal synchronizing signal data or vertical synchronizing signal data on input image signal data is performed. As for patterns of the synchronizing signals, various patterns are applied due to diversity of image signal formats.
As an image signal data generator in which a process of superposing synchronizing signals is performed as described above, one provided with ROMs 901 to 903 storing synchronizing signal data showing a synchronizing signal level for each prescribed timing, as shown in FIG. 11 for example, is well-known. In detail, the ROMs 901 to 903 store synchronizing signal data for respective image signal formats of plural types, and synchronizing signal data is read out corresponding to a horizontal counter value counted up at each prescribed timing. Among the pieces of synchronizing signal data outputted from respective ROMs 901 to 903, one of them is selected and outputted corresponding to an image signal format selecting signal by a selector 904.
The synchronizing signal data selected by the selector 904, and input image signal data to which synchronizing signal amplitude level data is added by an adder 905 are inputted into a selector 906, and a selection is performed according to a synchronizing signal generating pulse showing the synchronizing signal output period, whereby output image signal data, as shown in FIG. 12 for example, is outputted (see, for example, Japanese Patent Application Laid-open No. 2-268093 and Japanese Patent Application Laid-Open No. 3-113982). Here, the reason why the synchronizing signal amplitude level data is added to the input image signal data is to raise an input image signal, in which the black level is “0” in general, to the amplitude level of the synchronizing signal. More specifically, assuming that the value of the input image signal data is 0 to 255 and the value of the synchronizing signal amplitude level data is 0 to 8 (that is, the maximum value is 8), for example, the maximum value becomes the black level for the output image signal data, whereby a process of adding 8 to the input image signal data is performed by the adder 905.
However, in the conventional image signal data generator as described above, synchronizing signal data directly showing the synchronizing signal level is stored on the ROMs 901 to 903, whereby the amount of data is large, which may cause a problem of increasing the circuit scale and the manufacturing cost. This problem becomes more prominent along with the diversity of image signal formats. Further, in such a configuration that synchronizing signal data is selected by the selector 906 and made to be the output image signal data as described above, the adder 905 must be provided in order to conform the black level of the input image signal data to the synchronizing signal data. This may also cause an increase in the circuit scale and the manufacturing cost.